It's funny you mention this...I was talking with a friend of mine about starting to do the same thing, but we were going to do motorcycle parts, quad parts, and car parts as well. I have a bunch of friends who own or know people who own motorcycles and quads, and business could be boomin' as long as I can get the right materials for the job and be able to produce a good quality coating. We'll see though.... I'm with loco and RNBRAD on this one, if you know a lot of people locally that would be interested in having you powdercoat their stuff, go for it. I wouldn't stick to just quads though, that would seriously limit you to what you "could" make in profits.
It's a great idea... I know there is only one, maybe two powdercoaters here in Memphis which was what gave me the idea to do the same as you
Good luck to ya!!